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United States Patent |
5,772,771
|
Li
,   et al.
|
June 30, 1998
|
Deposition chamber for improved deposition thickness uniformity
Abstract
An improved deposition chamber (2) includes a housing (4) defining a vacuum
chamber (18) which houses a substrate support (14). A set of first nozzles
(34) have orifices (38) opening into the vacuum chamber in a
circumferential pattern spaced apart from and generally overlying the
periphery (40) of the substrate support. One or more seconds nozzle (56,
56a), positioned centrally above the substrate support, inject process
gases into the vacuum chamber to improve deposition thickness uniformity.
Deposition thickness uniformity is also improved by ensuring that the
process gases are supplied to the first nozzles at the same pressure. If
needed, enhanced cleaning of the nozzles can be achieved by slowly drawing
a cleaning gas from within the vacuum chamber in a reverse flow direction
through the nozzles using a vacuum pump (84).
Inventors:
|
Li; Shijian (San Jose, CA);
Redeker; Fred C. (Fremont, CA);
Ishikawa; Tetsuya (Santa Clara, CA)
|
Assignee:
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Applied Materials, Inc. (Santa Clara, CA)
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Appl. No.:
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571618 |
Filed:
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December 13, 1995 |
Current U.S. Class: |
118/723I; 118/715; 204/298.07 |
Intern'l Class: |
C23C 016/00 |
Field of Search: |
118/715,723 I,723 IR,723 E
204/298.07
315/111.51
156/345
|
References Cited
U.S. Patent Documents
3717439 | Feb., 1973 | Sakai | 118/715.
|
4716852 | Jan., 1988 | Tsujii et al. | 118/720.
|
4817558 | Apr., 1989 | Itoh | 118/725.
|
5069930 | Dec., 1991 | Hussla et al. | 427/55.
|
5105761 | Apr., 1992 | Charlet et al. | 118/723.
|
5192370 | Mar., 1993 | Oda et al. | 118/723.
|
5250092 | Oct., 1993 | Nakano | 96/136.
|
5346578 | Sep., 1994 | Benzing et al. | 156/345.
|
5368646 | Nov., 1994 | Yasuda et al. | 118/723.
|
5522934 | Jun., 1996 | Suzuki et al. | 118/723.
|
5525159 | Jun., 1996 | Hama et al. | 118/723.
|
5532190 | Jul., 1996 | Goodyear et al. | 437/225.
|
5554226 | Sep., 1996 | Okase et al. | 118/724.
|
5614055 | Mar., 1997 | Fairbairn et al. | 156/345.
|
5620523 | Apr., 1997 | Maeda et al. | 118/723.
|
Foreign Patent Documents |
0 308 946 A2 | Mar., 1989 | EP.
| |
61-263118 | Nov., 1986 | JP.
| |
197803 | Mar., 1978 | SU.
| |
Other References
Kaplan et al, Deposition Method for Aluminum Oxide Films,IBM Technical
Disclosure Bulletin vol. 7 No. 5, pp. 414-415, Oct. 1964.
|
Primary Examiner: Breneman; R. Bruce
Assistant Examiner: Lund; Jeffrie R.
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP
Claims
What is claimed is:
1. A deposition chamber comprising:
a housing defining a single vacuum chamber;
a substrate support having a substrate support surface within the vacuum
chamber, the substrate support surface having a central region and a
periphery;
a plurality of first gas distributors having first exits opening into the
vacuum chamber, the first exits directed generally towards the central
region;
a second gas distributor having a second exit spaced apart from and
generally overlying said substrate support surface, said second exit
opening directly into the vacuum chamber; and
said first gas distributors being located closer to the support surface
than are the second gas distributors.
2. The chamber according to claim 1 further comprising inductive coils
mounted to the housing and coupled to a radio frequency generator.
3. The chamber according to claim 1 wherein the periphery is generally
circular.
4. The chamber according to claim 1 wherein the first gas distributors
include a plurality of nozzles equally spaced about the center of the
substrate support surface.
5. The chamber according to claim 1 wherein the second gas distributor
includes a second nozzle and said second exit includes a single orifice.
6. The chamber according to claim 1 wherein the second gas distributor
includes a plurality of second nozzles and said second exit includes a
plurality of orifices.
7. The chamber according to claim 1 wherein the second gas distributor is
spaced apart from the support surface by a distance at least twice as
great as a distance between the support surface and any one of the first
gas distributors.
8. The chamber according to claim 1 further comprising a gas manifold
fluidly coupled to the first gas distributors.
9. The chamber according to claim 8 further comprising means for helping to
supply gas to the first gas distributors at substantially the same
pressure.
10. The chamber according to claim 9 wherein the helping means comprises a
plurality of equal diameter, equal length gas supply lines fluidly coupled
to the manifold at different positions along the manifold.
11. The chamber according to claim 9 wherein the helping means comprises a
plurality of gas supply lines fluidly coupled to the manifold at different
positions along the manifold, each gas supply line constructed to provide
equal resistance to fluid flow.
12. The chamber according to claim 1 further comprising:
a vacuum pump having an inlet and an outlet;
a passageway fluidly coupling the inlet to at least one of the first and
second gas distributors; and
a flow control assembly controlling fluid flow along the passageway so that
a cleaning gas within the vacuum chamber can be drawn from the vacuum
chamber and through the at least one of the first and second gas
distributors in a controlled manner so to ensure effective cleaning of the
distributors.
13. The chamber according to claim 12 wherein the vacuum pump is a roughing
pump.
14. The chamber according to claim 12 wherein the flow control assembly
comprises a shutoff valve along the passageway and a flow controller along
the passageway between the shutoff valve and the vacuum pump.
Description
BACKGROUND OF THE INVENTION
One of the primary steps in the fabrication of modern semiconductor devices
is the formation of a thin film on a semiconductor substrate by chemical
reaction of gases. Such a deposition process is referred to as chemical
vapor deposition (CVD). Conventional thermal CVD processes supply reactive
gases to the substrate surface where heat-induced chemical reactions can
take place to produce the desired film. High density plasma CVD processes
promote the disassociation of the reactant gases by the application of
radio frequency (RF) energy to the reaction zone proximate the substrate
surface thereby creating a plasma of highly reactive ionic species. The
high reactivity of the released ionic species reduces the energy required
for a chemical reaction to take place, and thus lowers the required
temperature for such CVD processes.
In one design of high density plasma chemical vapor deposition (HDP-CVD)
chambers, the vacuum chamber is generally defined by a planar substrate
support, acting as a cathode, along the bottom, a planar anode along the
top, a relatively short sidewall extending upwardly from the bottom, and a
dielectric dome connecting the sidewall with the top. Inductive coils are
mounted about the dome and are connected to a supply radio frequency
generator. The anode and the cathode are typically coupled to bias radio
frequency generators. A series of equally spaced gas distributors,
typically nozzles, are mounted to the sidewall and extend into the region
above the edge of the substrate support surface. The gas nozzles are all
coupled to a common manifold which provides the gas nozzles with process
gases, including gases such as argon, oxygen, silane, TEOS
(tetraethoxysilane), silicon tetrafluoride (SiF.sub.4), etc., the
composition of the gases depending primarily on what type of material is
to be formed on the substrate. The nozzle tips have exits, typically
orifices, positioned in a circumferential pattern spaced apart above the
circumferential periphery of the substrate support and through which the
process gases flow.
The thickness of the deposited film is ideally, but in practice is never,
perfectly uniform. Deposition uniformity is very sensitive to source
configuration, gas flow changes, source radio frequency generator current,
bias radio frequency generator currents, the nozzle height above the
substrate support and the lateral position of the nozzle relative to the
substrate support. Improvements in this deposition uniformity are hindered
by several factors. For example, it is often preferable that the height of
the nozzles above the substrate support surface be greater than it is.
However, for practical reasons it is not feasible to position the nozzles
through the dielectric dome. Also, adjusting the height of the nozzles
above the substrate for each process condition is not practical unless the
substrate is movable vertically. Furthermore, while increasing the
distance between nozzle orifices and the substrate tends to improve the
deposition uniformity, it adversely affects the gas efficiency, that is
requires the use of more gas or more time. In addition, argon is commonly
directed through the manifold and nozzles as part of the process gases,
argon flow contributing to the effectiveness of sputtering rate and
sputtering uniformity. However, the use of argon restricts the flexibility
one has in varying the flow rate of the process gases through the nozzles.
Another factor affecting deposition is related to the cleanliness of the
nozzle orifices. Some process gases, such as silane, can thermally
disassociate and deposit silica on the inside of the nozzle orifices. In
addition, some oxygen may diffuse back into the nozzle orifices and react
with the process gases to create a deposit on the inside of the nozzle
orifices. Attempts to "dry clean" the chamber (by keeping the chamber
closed and injecting a cleaning gas, such as fluorine compounds, into the
chamber) can create additional problems. For example, fluorine gas can
partially react with deposited silica and create a porous material which
expands and clogs up the orifices even worse.
SUMMARY OF THE INVENTION
The present invention is directed to an improved deposition chamber which
uses a supplemental or second gas distributor, typically a nozzle,
centered above the substrate support surface to enhance deposition
thickness uniformity. Deposition thickness uniformity is also enhanced by
equalizing the pressure of the process gases supplied to a series of gas
distributors, also typically nozzles, fed by a common manifold.
The improved deposition chamber includes a housing defining a vacuum
chamber. A substrate support is housed within the vacuum chamber. A
plurality, typically 12, of first gas distributors, typically nozzles,
have their orifices or other exits opening into the vacuum chamber in a
circumferential pattern spaced apart from and generally overlying the
circumferential periphery of the substrate support surface, as is
conventional. With the invention, a second gas distributor is used and is
positioned spaced apart from and generally overlying the center of the
substrate support surface. The use of the second gas distributor to inject
process gases into the vacuum chamber helps to improve deposition
thickness uniformity over that which is achieved without the use of the
second gas distributor.
Deposition thickness uniformity is also improved by supplying the process
gases to the manifold at a plurality of positions. The supply of the
process gases to the manifold is done in a manner so that the process
gases are supplied to the gas distributors at the same pressure. This is
done to ensure an equal flow rate from each of the first gas distributors.
The exits of the gas distributors are preferably sized to permit effective
dry cleaning operations. In some situations dry cleaning operations may
not be effective to clean the inside surfaces of the exits. In such
situations enhanced cleaning of the gas distributors can be achieved by
selectively connecting a vacuum pump to the gas distributors and slowly
drawing the cleaning gas within the vacuum chamber in a reverse flow
direction from the chamber, through the gas distributors and from the
system through the vacuum pump.
A primary advantage of the invention is that by independently supplying
process gases to the second (or upper) gas distributor, a more uniform
deposition thickness can be achieved under a variety of operating
conditions, which result in a change in the distribution of the process
gases through the first or lower gas distributors.
It has been found that a second gas distributor with a single exit is
effective for use with 8-inch (20 cm) substrates. However, for larger
substrates, such as 12-inch (30 cm) substrates, one or more second gas
distributors having a plurality of exits will likely provide the best
deposition thickness uniformity.
Other features and advantages of the invention will appear from the
following description in which the preferred embodiment has been set forth
in detail in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view showing a deposition chamber
made according to the invention;
FIG. 1A is a simplified view of an alternative embodiment of the center
nozzle of FIG. 1 having three orifices finding particular utility for use
with larger diameter (e.g., 12-inch or 30 cm) substrates;
FIG. 2 is an exaggerated view illustrating the characteristic M-shaped,
deposition thickness variation plot of the prior art;
FIG. 3 illustrates an improvement in the deposition thickness variation
plot of FIG. 2 using the apparatus and method according to the invention;
FIG. 4 is a schematic diagram illustrating a pair of equal length gas feed
lines used to supply the manifold with the process gases at equal
pressures; and
FIG. 5 is a schematic diagram illustrating how a cleaning gas within the
chamber can be drawn back through the nozzles using a vacuum pump.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a deposition chamber 2 comprising a housing 4, the
housing including a dielectric dome 6 surrounded by RF inductive coils 8.
Coils 8 are powered by a source RF generator 10 through a matching circuit
12. Chamber 2 also includes a substrate support 14 having a substrate
support surface 16 within the vacuum chamber 18 defined within housing 4.
Surface 16 is used to support a substrate 20 within chamber 18. Substrate
support 14 acts as a cathode and is connected to a bias RF generator 22
through a matching circuit 24. The top 25 of housing 4 acts as an anode
and is electrically biased by a second bias RF generator 26 through a
matching circuit 28. A generally cylindrical sidewall 30 of housing 4
connects the bottom 32 of housing 4 to dielectric dome 6. Process gases,
typically including deposition gases such as silane, TEOS, silicon
tetrafluoride (SiF.sub.4) and any other reactive deposition gas which has
a short lifetime in chamber 18, as well as process gases such as argon,
are introduced to vacuum chamber 18 through a series of 12 equally spaced
nozzles 34. As suggested in FIG. 4, nozzles 34 are arranged in a ring-like
pattern and are all fluidly coupled to a gas manifold 36. Each nozzle 34
has an orifice 38 at its distal end. The orifices 38 of nozzles 34 are
arranged above the periphery 40 of substrate support 14 and thus above the
periphery 42 of substrate 20 since the two peripheries are generally
aligned. Vacuum chamber 18 is exhausted through an exhaust port 44.
The above-described structure of deposition chamber 2 is described in more
detail in U.S. patent application Ser. No. 08/234,746 filed Apr. 26, 1994,
the disclosure of which is incorporated by reference.
FIG. 2 illustrates a typical deposition thickness variation plot 46 for a
conventional deposition chamber as described above. The average thickness
is shown by base line 48. As can be seen by this plot 46, there is a
relatively steep increase in thickness at end points 50 and 52 of plot 46
corresponding to the periphery 42 of substrate 20. The center 54 of plot
46 also dips down substantially as well.
The present invention improves upon plot 46 through the use of a center
nozzle 56 coupled to a second gas source 58 through a second gas
controller 60 and a second gas feed line 62. See FIGS. 1 and 4. Center
nozzle 56 has an orifice 64 positioned centrally above substrate support
surface 16. Orifice 64 is positioned at least twice the distance from
surface 16 as are orifices 38 of nozzles 34. Using center nozzle 56
permits the modification of deposition thickness variation plot 46 from
that of FIG. 2 to exemplary plot 68 of FIG. 3. Exemplary deposition
thickness variation plot 68 is flat enough so that the standard deviation
of the deposition thickness is about 1 to 2% of one sigma. This is
achieved primarily by reducing the steep slope of the plot at end points
50, 52 and raising in the low point at center 54 of plot 46.
In the preferred embodiment, 12 identical nozzles 34 are used in the
regions surrounding periphery 40 of substrate support 14. Orifices 38 have
a diameter of about 0.014 inch (0.36 mm) and a depth or throat of about
0.020 inch (0.51 mm). It has been found that enlarging the orifice
diameter and limiting the depth or throat of orifice 38 is important in
ensuring that cleaning gases defuse back into the nozzles during dry clean
operations. Such consideration may not be as necessary when the nozzle
cleaning system described with reference to FIG. 5 is used.
To help ensure that equal amounts of processing gases pass through each
orifice 38, it is useful to provide the processing gases at the same
pressure to each nozzle 34. To help do so, the processing gas is provided
to manifold 36 at opposite sides of the manifold as shown in FIG. 4.
Manifold 36 is supplied by a pair of gas feed lines 70, 72, which are
coupled to a first gas controller 74 and a first gas source 76 as shown in
FIG. 4. Gas feed line 70, 72 are constructed so as to be of equal lengths
and equal diameters to provide equal resistance to fluid flow for the
processing gases entering manifold 36. Other ways for helping to ensure
the same amount of processing gas flows through nozzles 34 could be used.
For example, manifold 36 could be modified so that it is actually two
manifolds, an outer manifold (not shown) coupled to one or more of the gas
feed lines 70, 72 and having openings (not shown) opening into a inner
manifold (not shown) to which first nozzles 34 are mounted. The openings
coupling the outer and inner manifolds could be smaller adjacent the
entrances of gas feed lines 70, 72 and larger away from those entrances to
help equalize the flow rates to first nozzles 34.
While deposition chamber 2 is suitable for dry cleaning operations, the
system shown with reference to FIG. 5 can be used to help ensure proper
cleaning of the nozzles. A process gas valve 78 is used along common gas
feed line 80 operates as a final valve so to isolate vacuum chamber 18
from first gas controller 74 during cleaning operations. Downstream of
process gas valve 78, that is between the process gas valve 78 and
manifold 36, is a cleaning gas line 82 coupling a vacuum pump 84 to common
gas feed line 80 through a flow control valve 86 and a shutoff valve 88,
valves 86, 88 acting as a flow control assembly 90. For cleaning nozzles
34, valve 78 is closed, a cleaning gas is introduced into vacuum chamber
18, shutoff valve 88 is opened and flow control valve 86 is operated to
permit vacuum pump 84 to slowly draw the cleaning gas into nozzles 34
through orifices 38, back through manifold 36 and along line 82 through
the operation of vacuum pump 84. In this way, cleaning of the insides of
nozzles 34 is not left to the ability of the cleaning gases to diffuse
into the interior of the nozzles through their orifices 38 but rather are
actively, albeit slowly, drawn through the orifices and into the nozzles
by vacuum pump 84.
In use, the operator can affect or control the deposition thickness
uniformity occurring on substrate 20 by controlling the discharge of
process gases through center nozzle 56 independently of the passage of the
same or different process gases through nozzles 34. Thickness uniformly is
also enhanced by helping to equalize the flow through each orifice 38 into
vacuum chamber 18, preferably by delivering the gases to the manifold 36
using two or more gas feed lines 70, 72, each gas feed line exhibiting a
common fluid flow resistance from a common gas source 76. After a period
of time, it may be desired to clean deposition chamber 2 using various
cleaning gases within vacuum chamber 18. Orifices 38 and the remainders of
the interiors of nozzles 34 can be effectively cleaned by using vacuum
pump 84, typically a roughing pump, to slowly draw the cleaning gases in a
retrograde or reverse manner through orifices 38 and into the interiors of
nozzles 34, into manifold 36 and finally from chamber 2.
In the preferred embodiment maximum flexibility is achieved using two gas
controllers 60, 74 and two separate gas sources 58, 76 since this permits
both the composition and rate of gas flow through nozzles 34, 56 to be
independently varied. If the same gas composition is to be used for
nozzles 34, 56, a single gas source, a single gas controller and a flow
divider could be used to supply the gas to lines 62, 80.
The above-described embodiment has been designed for substrates 20 having
diameters of 8 inches (20 cm). Larger diameter substrates, such as
substrates having diameters of 12 inches (30 cm), may call for the use of
multiple center nozzles 56a as illustrated in FIG. 1A. In such embodiments
the deposition thickness variation plot would likely have a three-bump (as
in FIG. 3), a four-bump or a five-bump shape. The particular shape for the
deposition thickness plot would be influenced by the type, number,
orientation and spacing of center nozzles 56A and orifices 64.
Modification and variation can be made to the disclosed embodiment without
departing from the subject of the invention as defined in the following
claims. For example, center nozzle 56 could be replaced by a shower head
type of gas distributor having multiple exits. Similarly, nozzles 34 or
nozzles 56a could be replaced by, for example, a ring or ring-like
structure having gas exits or orifices through which the process gases are
delivered into chamber 18.
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